Cavity resonator delay circuit having interdigitally supported drift tubes and a continuous undulating conductor



April 25, 1967 LEBQUTET ET AL 3,316,440

CAVITY RESONATOR DELAY CIRCUIT HAVING INTERDIGITALLY SUPPORTED DRIFT TUBES AND A CONTINUOUS UNDULATING CONDUCTOR Filed June 28, 1963 2 Sheets-Sheet 1 m D If) no v u m \J Q Q\\ CD IO LL FIG.1

FIG.4

United States Patent 3,316,440 CAVITY RESONATOR DELAY CIRCUIT HAVING INTERDIGITALLY SUPPORTED DRIFT TUBES l rgo A CONTINUOUS UNDULATING CONDUC- R Hubert Leboutet and Germaine Vincent, both of 79 Blvd. Haussmann, Paris, France Filed June 28, 1963, Ser. No. 291,337 Claims priority, application France, July 4, 1962, 902,897 12 Claims. (Cl. 315-5) The present invention relates to a novel resonant cavity and to the devices susceptible to utilize one or several of these cavities, such as, for example, velocity modulation tubes conceived to operate as hyperfrequency amplifiers or oscillators, or particle accelerators.

It is already known to utilize resonant cavities in the devices of this nature; the object of the present invention is, however, a cavity such that in comparison with the devices utilizing the known cavities one obtains, with equality of dimensions, improved electrical characteristics insofar as the shunt resistance and the Q factor are concerned, or, with equality of electrical performances, more reduced dimensions.

The cavity according to the present invention comprises an envelope having an axis of symmetry, for example, of rectangular, elliptical, or other suitable circular cross section, a series of constant pitch or variable pitch drift tubes disposed along the axis of symmetry, these tubes being supported by rods disposed within a plane passing through this axis and secured alternately to one of the opposite points along the envelope, these rods thus forming an interdigital structure within an axial plane of the envelope, and a conductor on the inside of the envelope, this conductor having the extremities thereof secured to the end or frontal faces of the envelope and being bent into a meandering or undulating shape extending along the said axis in such a manner as to pass in slalom fashion between the said drift tubes, whereby the plane of meander or undulations may coincide with any selected plane depending on the desired Q of the cavity; for example, this plane may be that of the said system of the rods, whereby the Q of the cavity is then a maximum, or that of the plane perpendicular thereto whereby the Q of the cavity then becomes a minimum, or any inclined plane intermediate these two planes and suitably chosen, piercings or apertures for the passage of the beam being provided within this conductor at the successive intersections of the undulations or meander with the said axis.

Accordingly, it is an object of the present invention to provide resonant cavity structures that exhibit superior characteristics over those known heretofore in the prior art, yet are simple to manufacture and assemble.

Another object of the present invention resides in the provision of resonant cavity structures which, with the equality of dimensions, assure improved electrical characteristics as regards shunt resistance and Q factor thereof compared to the prior art devices.

Still a further object of the present invention resides in the provision of resonant cavity structures which, with equality in electrical performance, permit a reduction in the dimensions thereof.

These and other objects, features and advantages of the present invention will become more obvious from the fol- ICC lowing description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, several embodiments in accordance with the present invention, and wherein:

FIGURE 1 is a longitudinal cross sectional view of a first embodiment of a cavity according to the present invention,

FIGURE 2 is a transverse cross sectional view of the cavity illustrated in FIGURE 1, taken along line II-II thereof,

FIGURE 3 is a longitudinal cross sectional vieW of a modified embodiment of a cavity according to the present invention,

FIGURE 4 is a longitudinal cross sectional view through the embodiment of the cavity structure of FIGURE 3, taken at right angle thereto along the line IVIV,

FIGURE 5 is a diagram illustrating a characteristic curve for a cavity of the type illustrated in FIGURES 3 and 4,

FIGURE 6 is a schematic diagram of a particle accelerator utilizing cavities in accordance with the present invention, and

FIGURE 7 is a longitudinal cross sectional view through a hyperfrequency electron tube utilizing a cavity according to the present invention.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to FIGURES 1 and and 2, the cavity illustrated therein comprises a parallelepipedic envelope 1 of which an axis 2 is chosen as longitudinal axis. With respect to this axis, the envelope 1 comprises two rectangular frontal or end faces of which the cross sections are EF and GH, two large lateral faces of which the cross sections are AB and CD, and two small lateral faces of which the cross sections are AC and BD. Along the axis 2 is disposed a chain of hollow cylinders 3 which may have either a constant or variable pitch, these cylinders 3 being supported by the rods 4, secured alternately to each of the large opposite lateral faces AB and CD. The system of rods 4 thus forms an interdigital structure within the axial plane parallel to the small lateral faces AC and BD. A conductor 5, having the extremities thereof fixed or secured to the frontal faces of the cavity in any suitable manner, is bent into an undulating or meandering shape, for example, in the plane of the rods 4, and is disposed to pass in slalom fashion between the cylinders 3, that is undulating to and fro between the cylinders 3 as shown in FIGURE 1. At the places of intersection of the to and fro undulations with the axis 2, the conductor 5 is pierced by apertures 6 for the passage of the beam. Similarly, the frontal faces EF and GH comprise within the axis 2 apertures 7 that permit the entry and exit of the beam into and from the cavity, re spectively.

The cavity illustrated in FIGURES 3 and 4, in which the same reference numerals have been employed to designate analogous elements, and in which the system of rods 4 is still situated within the axial plane parallel to the small lateral faces AC and BD, differs from the emperpendicular thereto, that is within the axial plane paral- 3 lel to the large lateral faces AB and CD. Otherwise, this cavity is identical to that of the preceding embodiment.

Both theory and experiments have indicated that following the schematic arrangement of the principle illustrated in FIGURES 3 and 4, one may realize, for example, a cavity operating at a frequency of 67 mHz. withthe following characteristics: length, 1.80 m.; transverse cross section, 0.5 1.60 m.; number of tubes 3, approximately 50.

FIGURE 5 shows for such a cavity the characteristic by plotting along the ordinates the shunt resistance R in megohms/ cm. and along the abscissae the delay ratio v, where c=speed of light, and v=phase velocity of the wave in the fundamental mode at the frequency of 67 mHz. This characteristic shows high values for R in the neighborhood of 50 megohms/cm., within the particularly interesting band of c/v between 2 and 6 approximately. Its Q factor becomes of the orderof magnitude of 20,000. The comparison with other known delay circuits, operating at the same frequency, show that with equal electric performances the encumberment and dimensions of the prior art structures are much greater, or that with comparable dimensions the electrical characteristics thereof are much more unfavorable.

FIGURE 6 represents schematically a particle accelerator, forexample, of heavy ions, utilizing cavities according to the present invention. In this application, the pitch of the delay circuit constituted by the drift tubes 3 and the undulating or meandering conductor 5, will be variable, as is well known, in order to maintain the condition of synchronism between the phase velocity of the wave and the velocity of the accelerated particles.

The accelerator illustrated in FIGURE 6 is composed essentially of the following elements, indicated only schematically since the details thereof, insofar as not shown herein, may be ofconventional, standard construction:

Of a source of particles 8, producing a beam 9;

Of a chain of cavities 1 which may be of the type of FIGURES l and 2 or of the type of FIGURES 3 and 4, or of a type intermediate these two embodiments in which the undulations or meander of the conductor are comprised within an inclined plane suitably chosen and of any desired value;

And of a target'10.

Between the cavities 1 of the chain are provided drift spaces 11 of which one takes advantage to dispose the windings 12 for the magnetic focusing system.

The cavities 1 are excited from ultra-high frequency generators 13 by the intermediary of coupling loops 14. The frequency of these generators may be the same for all of the cavities or one may also employ different frequencies suitably distributed along the chain.

The cavities are individually connected to pumps 15.

FIGURE 7 represents another example of application of the present-invention, particularly to hyperfrequency electron tubes. In particular, the embodiment of FIG- URE 7 shows a backward wave oscillator or so-called Carcinotron oscillator tube.

In this example, a cavity of the type, for example, of FIGURES 1 and 2 of which the drift tubes 3 and the undulating or meandering conductor have been designated by the same reference numerals, is incorporated within the envelope1-6 to which are connected on one side of the collector 17 and on the other side the base 1 8 containing an electron gun 19 furnishing a beam 20. e The delay circuit, having a constant pitch, is covered within the regions adjacent the collector 17 with an attenuation 21 intended to absorb the direct wave and to cause the tube to operate as travelling wave tube, the anode voltage being such that the circuit is utilized on an inverse or backward mode. An output coupling loop 22 is disposed on the side of the gun 19. The windings 23 produce the magnetic focusing field.

While a backward wave oscillator or Carcinotron tube is illustrated in FIGURE 7, it is understood however,

that the application of the present inventiomis not limited thereto but is equally applicable to any other hyperfrequency electron tube with the same application. In particular, one can cause the delay circuit to operate on a direct mode and to realize an amplifier with an input coupling loop at the gun side and an output loop at the side of the collector, whereby the attenuation is disposed at a place suitable for the amplifiers as is known in the prior art.

Thestructure of the cavity described admits itself numerous modifications as known to a person skilled in the art. For example, the apertures within the undulating or meandering conductor may be replaced by rings analogous to the drift tubes 3, inserted along the path of the conductor 5. However, it must be understood that the cavities that have undergone such modifications which do not alter in principle the structure thereof nor the possibility of the different applications thereof not specifically described herein, form equally part of the present invention.

Thus, while we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications within the spirit and scope thereof, and we therefore do not wish to bevlimited to the details shown and described herein but intended to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1.:A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located substantially along said axis, each of said drift tubes being supported by rod-shaped elements, said rod-shaped elements being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby forming a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive drift tubes withina plane passing substantially through said axis and having its extremities fixed to said envelope, and means to enable propagation of a particle beam along said axis of symmetry through the drift tubes of said cavity.

2. A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at least one axis of symmetry and of substantially rectangular cross section, a. series'of drift tubes located substantially along said axis, each of said drift tubes being supported by rod-shaped elements, said rod-shaped ele ments being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby forming a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive drift tubes within a plane passing substantially through said axis and having its extremities fixed to said envelope, and means to enable propagation of a particle beam along said axis of symmetry through the drift tubes of said cavity.

3. A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located substantially along said axis and periodically spaced with a constant pitch, each of said drift tubes being supported by rod-shaped elements, said rod-shaped elements being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby forming a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive drift tubes within 1 ing its extremities fixed to said envelope, and means to enable propagation of a particle beam along said axis of symmetry through the drift tubes of said cavity.

4. A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at least one axis of symmetry, aseries of drift tubes located substantially along said axis with a progressively varying spacing therebetween, each of said drift tubes being supported by rod-shaped elements, said rodshaped elements being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby forming a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive drift tubes within a plane passing substantially through said axis and having its extremities fixed to said envelope, and means to enable propagation of a particle beam along said axis of symmetry through the drift tubes of said cavity.

5. A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located substantially along said axis, each of said drift tubes being supported by rod-shaped elements, said rodshaped elements being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby forming a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive drift tubes within a plane passing substantially through said axis and having its extremities fixed to said envelope, the the plane of said woven conductor being substantially common with the plane of said interdigital structure.

6. A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located substantially along said axis, each of said drift tubes being supported by rod-shaped elements, said rod-shaped elements being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby form-ing a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive drift tubes within a plane passing substantially through said axis and having itsextremities fixed to said envelope, the plane of said woven conductor being substantially perpendicular to the plane of said interdigital structure.

7. A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located substantially along said axis, each of said drift tubes being supported by rod-shaped elements, said rod-shaped elements being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby forming a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive drift tubes within a plane passing substantially through said axis and having its extremities fixed to said envelope, and means to enable propagation of a particle beam along said axis of symmetry through said tubes including apertures provided in said woven conductor along said axis.

8. A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at -least one axis of symmetry, a series of drift tubes located substantially along said axis, each of said drift tubes being supported by rod-shaped elements, said rod-shaped elements being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby forming a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive drift tubes within a plane passing substantially through said axis and having its extremities fixed to said envelope, and means to enable propagation of a particle beam along said axis of symmetry through said tubes including apertures provided in said woven conductor at points of intersection with said axis, means for establishing a standing microwave pattern within said cavity along said axis, and means for propagating travelling microwave energy through said circuit along said axis.

9. A delay circuit for particle beam devices, comprising at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located substantially along said axis, each of said drift tubes being supported by rod-shaped elements, said rod-shaped elements being approximately situated within a common plane passing substantially through said axis and being alternately fixed to opposite points of said envelope thereby forming a substantially interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between successive dift tubes within a plane passing substantially through said axis and having its extremities fixed to said envelope.

10. A linear particle accelerator, comprising a delay circuit including at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located along said axis with progressively varying spacing between them, each of said tubes being supported by rod-shaped elements, said rod-shaped elements being situated approximately in a common plane passing through said axis and being alternately fixed to opposite points of said envelope thereby forming an interdigital structure in an axial plane of said envelope, and a continuous conductor woven to and fro passing between said successive tubes in a plane passing substantially through said axis and having its extremities fixed to said envelope, means for propagating micro-wave energy along said circuit, means for propagating a particle beam along said axis of symmetry through said tubes thereby accelerating said particles by interaction with said microwave energy, and means for collecting said accelerated particles.

=11. An electron tube, comprising a delay circuit including at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located along said axis with a substantially constant" spacing therebetween, each of said tubes being supported by rod-shaped elements, said rod-shaped elements being situated approximately in a common plane passing through said axis and being alternately fixed to opposite points of said envelope thereby forming an interdigital structure in an axial plane of said envelope, and a circuit including a continuous conductor Woven to and fro passing between said successive tubes in a plane passing through said axis and having its extremities fixed to said envelope, means for propagating an electron beam along said axis of symmetry through said tubes, and means for abstracting microwave energy from said circuit.

12. An electron tube, comprising a delay circuit including at least one cavity resonator bounded by an envelope having at least one axis of symmetry, a series of drift tubes located along said axis with a substantially constant spacing therebetween, each of said tubes being supported by rod-shaped elements, said rod-shaped elements being situated approximately in a common plane passing through said axis and being alternately fixed to opposite points of said envelope thereby forming an interdigital structure in an axial plane of said envelope, and a circuit including a continuous conductor woven to and fro passing between said successive tubes in a plane passing through said axis and having its extremities fixed to said envelope, attenuating means associated with said circuit covering a portion of said conductor means for propagating an electron beam along said axis of symmetry through said tubes, and means for abstracting microwave enengy from said circuit.

References Cited by the Examiner UNITED STATES PATENTS 7/1953 Touraton et a1. 3155.39 X 2,683,216 7/1954- Wideroe 328-233 8 2,768,322 10/1956 Fletcher 3153. 5 2,770,755 11/1956 Good 315--5.42 2,885,641 5/ 1959 Birdsall et a1. 333-31 3,067,359 12/1962 Pottier 3155.42

ELI LIEBERMAN, Primary Examiner.

"HERMAN G, SAALBACH, Examin r. s. CHATMON, 1a., Assistant Examiner;

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,316,440

Hubert Leboutet et a1 April 25, 1967 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below In the heading to the printed specification, lines 6 and 7, for "Hubert Leboutet and Germaine Vincent, both of 79 Blvd. Haussmann, Paris, France" read Hubert Leboutet and Germaine Vincent, both of Paris, France, ass ignors to CSF-Compagnie Generale De Telegraphie Sans Fil, Paris, France Signed and sealed this 21st day of November 1967 (SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A DELAY CIRCUIT FOR PARTICLE BEAM DEVICES, COMPRISING AT LEAST ONE CAVITY RESONATOR BOUNDED BY AN ENVELOPE HAVING AT LEAST ONE AXIS OF SYMMETRY, A SERIES OF DRIFT TUBES LOCATED SUBSTANTIALLY ALONG SAID AXIS, EACH OF SAID DRIFT TUBES BEING SUPPORTED BY ROD-SHAPED ELEMENTS, SAID ROD-SHAPED ELEMENTS BEING APPROXIMATELY SITUATED WITHIN A COMMON PLANE PASSING SUBSTANTIALLY THROUGH SAID AXIS AND BEING ALTERNATELY FIXED TO OPPOSITE POINTS OF SAID ENVELOPE THEREBY FORMING A SUBSTANTIALLY INTERDIGITAL STRUCTURE IN AN AXIAL PLANE OF SAID ENVELOPE, AND A CONTINUOUS CONDUCTOR WOVEN TO AND FRO PASSING BETWEEN SUCCESSIVE DRIFT TUBES WITHIN A PLANE PASSING SUBSTANTIALLY THROUGH SAID AXIS AND HAVING ITS EXTREMITIES FIXED TO SAID ENVELOPE, AND MEANS TO ENABLE PROPAGATION OF A PARTICLE BEAM ALONG SAID AXIS OF SYMMETRY THROUGH THE DRIFT TUBES OF SAID CAVITY. 